Many motorized dermatomes are known in the prior art. Typical examples are described in U.S. Pat. No. 2,419,114 (Briegel), U.S. Pat. No. 2,457,772 (Brown), U.S. Pat. No. 2,787,272 (Groom), U.S. Pat. No. 3,412,732 (Simon), U.S. Pat. No. 3,428,045 (Kratzsch), U.S. Pat. No. 3,670,734 (Hardy), U.S. Pat. No. 3,820,543 (Vanjushin), and U.S. Pat. No. 4,917,086 (Feltovich). All of these devices are fundamentally similar, in that a sharp blade edge is placed in contact with skin and driven by the motor in an oscillatory fashion to create a sawing action. In order to move the blade edge back and forth, the rotational action of the drive motor is converted to more or less linear motion through the use of a number of linkages. A means is usually provided for permitting the blade to cut the skin to a pre-selected depth so that a thin layer of skin can be removed as the dermatome is moved forward.
The cutting characteristics of the dermatome are determined by the motion of the cutting blade. When a blade is cutting tissue, the only useful motion is purely linear. The sawing action of the blade along the axis of the blade edge provides the cutting action while the dermatome is moved forward against the skin to bring more tissue to bear on the blade edge. Any other motion of the blade contributes only to dulling the blade. If the blade is permitted to yaw about an axis perpendicular to the blade edge during its oscillation, the blade edge will be repeatedly pressed into the tissue and withdrawn from tissue during each cycle, having the effect of "hammering" the edge of the blade into a flatter and less sharp shape. If the blade pitches up and down in a direction perpendicular to the direction of the movement of the blade forward along the skin, the blade will be repeatedly scraped across the tissue, having an effect equivalent to "filing" the edge of the blade into a flatter and less sharp shape.
Sharpness of the blade edge is a major variable affecting the quality of tissue cutting and the characteristics of a dermatome. Most dermatomes provide a means for quickly replacing a dull blade during skin grafting surgery in recognition of the fact that blades quickly lose their sharpness. Despite similarities in the materials and process of manufacture of these blades, some dermatomes subjectively seem to remain sharper much longer than others. Loss of sharpness and wearing of the blade is primarily due to the motion of the blade against the tissue.
Relative linearity of blade motion and maintenance of blade sharpness are only two of the factors affecting the performance and ease of use of a dermatome. Another factor of major importance relates to the cleaning of a dermatome between uses, because an improperly or incompletely cleaned dermatome cannot be satisfactorily re-sterilized for reuse. The time, labor-intensivness and resulting quality of cleaning are important aspects of dermatome use and re-use. When a dermatome is used to cut and remove skin, a considerable amount of tissue, debris and other materials will come into contact with the dermatome. As the dermatome must be rigorously cleaned and then re-sterilized between uses, it is desirable that there be no opening in the external surface of the dermatome which allows tissue to come into contact with internal components of the drive mechanism of the dermatome, and which may allow tissue to become entrapped by the internal components of the drive mechanism of the dermatome. However, no dermatome known in the art provides a housing to enclose the internal components of the drive mechanism, which typically converts the rotational motion of a drive source into a more or less linear motion to drive the blade, while at the same time providing means for quickly and easily removing and replacing blades during usage. As a result, cleaning of prior art dermatomes typically requires removal of tissue and debris from the internal region of the dermatome surrounding components of the drive mechanism; such cleaning is very time-consuming and imperfect, resulting in increased labor costs and reduced quality associated with dermatome usage.
An improved dermatome would provide blade oscillation along a perfectly linear path defined by the edge of the blade of the dermatome, while preventing any other motions of the blade with respect to the dermatome body or housing. The blade of the dermatome would be designed to have a low replacement cost and the dermatome body or housing would include a means for quickly and easily replacing the blade during surgery or harvesting of skin from a donor. The drive mechanism would be contained within a housing having no open space in order to reduce the likelihood that tissue and debris would enter into the region of the drive mechanism.
Dermatomes described in the prior art have included a number of attempts to implement and combine some of these desirable characteristics. Brown (U.S. Pat. No. 2,457,772), Groom (U.S. Pat. No. 2,787,272), Simon (U.S. Pat. No. 3,412,732), Kratzsch (U.S. Pat. No. 3,428,045) and Vanjushin (U.S. Pat. No. 3,820,543) all show guide rods intended to limit the motion of a blade carrier to linear motion along a defined axis, to which the blade is attached. These prior-art devices include drive mechanisms which provide accurate translation of the rotational motion of the shaft of a motor into a linear motion of a blade carrier, but none includes means to assure that the dermatome blade engages the blade carrier such that the axis of linear motion of the blade carrier is exactly parallel to the axis of the blade edge. In addition, none of these prior-art dermatomes provides a housing which encloses and surrounds the drive mechanism to prevent the entry of tissue, skin lubricant, and other debris while at the same time permitting quick and easy blade replacement during usage.
The Padgett Dermatome (Padgett Instruments, Kansas) provides for linear motion of the blade by guiding the back edge of the blade against two steel pins, while constraining the blade from pitching motion by guiding it between the dermatome body and a removable width plate. Motion is imparted to the blade by a yoke which pivots on a fixed pin. The yoke, when driven by the motor, swings through a portion of an arc. A pin on the yoke fits into a hole in the blade, while a spring in the yoke holds the blade against the guide pins. Friction and vibration are generated, and efficiency is lost, in the linkage because the rotary motion of the motor is first converted into arcuate motion, and then into linear motion at the blade. This dermatome, while providing excellent linear blade motion, provides reasonably large amplitude blade motion through the use of a very large motor and head, which makes the device unwieldy. In addition, an open space in the dermatome head which enables the yoke pin to engage the blade also enables tissue, skin lubricant, and other debris to enter into the dermatome head and into the region surrounding the yoke and drive mechanism.
The Feltovich dermatome (U.S. Pat. No. 4,917,086) is very similar to the Padgett dermatome, but has a blade assembly comprised of a metal blade non-releasably attached to a thermoplastic blade carrier. The Feltovich dermatome does not include steel guide pins, as included in the Padgett dermatome, to keep the motion of the blade assembly purely linear. Although a smaller and lighter dermatome body and motor make the device easier to handle, the very small amplitude of motion of the blade assembly, as well as the significant non-linearity of motion of the blade assembly, result in a relatively poorer quality of cut, less cutting efficiency, and shorter blade life, for the reasons described above. Also, like the Padgett dermatome, the Feltovich dermatome has an indirect drive, with a yoke component between the motor and the blade assembly which describes an arcuate motion. The arcuate motion of the yoke component generates friction between the yoke and blade assembly, further reducing cutting efficiency, and produces vibration. Also, the motion of the yoke requires an open space in the dermatome head to enable a pin at the end of the yoke to engage the blade assembly, and this open space also enables tissue, skin lubricant, and other debris to enter into the dermatome head and into the region surrounding the yoke and drive mechanism of the Feltovich dermatome. In U.S. patent application Ser. No. 08/256,267, of which the present application is a continuation-in-part, a direct linear drive dermatome for improved cutting of tissue was described, comprising: a blade assembly, including a blade and a blade carrier; a rotational drive assembly; and a housing which engages the blade assembly to constrain the movement of any point on the blade assembly to bi-directional linear movement over a predefined linear range, wherein the engaged blade assembly forms a cover for the housing so that the housing in combination with the engaged blade assembly defines a closed space which surrounds the rotational drive assembly while the blade assembly moves over the predefined linear range. The present invention describes a dermatome having a blade assembly and an alternate drive assembly similar to that used in prior art dermatomes such as the Feltovich dermatome, and a housing which constrains the movement of any point on the blade assembly to bi-directional linear movement over a predefined linear range. In the present invention, the blade assembly in combination with the housing form a cover to define a closed space which surrounds the drive assembly while the blade assembly moves over the predefined linear range. The present invention can be readily implemented by adapting a prior-art dermatome, to produce an improved dermatome having a more linear drive, longer blade life, a better quality of cut and less tissue debris around the drive assembly.